// Copyright 2014 The Chromium Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

#ifndef NET_SPDY_HPACK_INPUT_STREAM_H_
#define NET_SPDY_HPACK_INPUT_STREAM_H_

#include <stddef.h>
#include <stdint.h>

#include <string>
#include <utility>

#include "base/macros.h"
#include "base/strings/string_piece.h"
#include "net/base/net_export.h"
#include "net/spdy/hpack/hpack_constants.h"
#include "net/spdy/hpack/hpack_huffman_table.h"

// All section references below are to
// http://tools.ietf.org/html/draft-ietf-httpbis-header-compression-08

namespace net {

namespace test {
    class HpackInputStreamPeer;
} // namespace test

typedef std::pair<size_t, uint32_t> InitialPeekResult;

// An HpackInputStream handles all the low-level details of decoding
// header fields.
class NET_EXPORT_PRIVATE HpackInputStream {
public:
    friend class test::HpackInputStreamPeer;

    explicit HpackInputStream(base::StringPiece buffer);
    ~HpackInputStream();

    // Returns whether or not there is more data to process.
    bool HasMoreData() const;

    // If the next bits of input match |prefix|, consumes them and returns true.
    // Otherwise, consumes nothing and returns false.
    bool MatchPrefixAndConsume(HpackPrefix prefix);

    // The Decode* functions return true and fill in their arguments if
    // decoding was successful, or false if an error was encountered.

    bool DecodeNextUint32(uint32_t* I);
    bool DecodeNextIdentityString(base::StringPiece* str);
    bool DecodeNextHuffmanString(std::string* str);

    // Stores input bits into the most-significant, unfilled bits of |out|.
    // |peeked_count| is the number of filled bits in |out| which have been
    // previously peeked. PeekBits() will fill some number of remaining bits,
    // returning the new total number via |peeked_count|. Returns true if one
    // or more additional bits were added to |out|, and false otherwise.
    bool PeekBits(size_t* peeked_count, uint32_t* out) const;

    // Similar to PeekBits, but intended to be used when starting to decode a
    // Huffman encoded string. Returns a pair containing the peeked_count and
    // out values as described for PeekBits, with the bits from the first N bytes
    // of buffer_, where N == min(4, buffer_.size()), starting with the high
    // order bits.
    // Should only be called when first peeking at bits from the input stream as
    // it does not take peeked_count as an input, so doesn't know how many bits
    // have already been returned by previous calls to InitializePeekBits and
    // PeekBits.
    InitialPeekResult InitializePeekBits();

    // Consumes |count| bits of input. Generally paired with PeekBits().
    void ConsumeBits(size_t count);

    // If not currently on a byte boundary, consumes and discards
    // remaining bits in the current byte.
    void ConsumeByteRemainder();

    // Return the total bytes that have been parsed SUCCESSFULLY.
    uint32_t ParsedBytes() const;

    // When incrementally decode the header, need to remember the current
    // position in the buffer after we successfully decode one opcode.
    void MarkCurrentPosition();

    // Returning true indicates this instance of HpackInputStream
    // doesn't have enough data to parse the current opcode, and we
    // are done with this instance. When more data arrive, a new
    // HpackInputStream should be created to restart the parsing.
    bool NeedMoreData() const;

private:
    base::StringPiece buffer_;
    size_t bit_offset_;
    // Total number of bytes parsed successfully. Only get updated when an
    // opcode is parsed successfully.
    uint32_t parsed_bytes_;
    // Total number of bytes parsed currently. Get updated when an octet,
    // a number or a string has been parsed successfully. Can point to the
    // middle of an opcode.
    uint32_t parsed_bytes_current_;
    bool need_more_data_;

    bool PeekNextOctet(uint8_t* next_octet);

    bool DecodeNextOctet(uint8_t* next_octet);

    DISALLOW_COPY_AND_ASSIGN(HpackInputStream);
};

} // namespace net

#endif // NET_SPDY_HPACK_INPUT_STREAM_H_
